In recent years, an Ultra Wide Band (UWB) has drawn attention as a new communication means. UWB transmits amounts of data using a broad frequency band over a short distance such as 10 m or 33 feet. A frequency band of 3.1 to 10.6 GHz, for example, is subjected to use for UWB according to the rule of U.S. FCC (Federal Communication Commission). As such, a feature of UWB is to utilize a broad frequency band. Japan and the ITU-R have a plan to introduce standards separated into a low band of about 3.1 to 4.7 GHz and a high band of about 6 GHz to 10.6 GHz to avoid a band of 5.3 GHz that is used in the IEEE802.11a standard. Accordingly, a low band filter requires the characteristic of being abruptly attenuated at 2.5 GHz and 5.3 GHz.
Therefore, there is a need for a bandpass filter which can receive a differential signal and is applicable for a UWB, and which has an attenuation pole near both sides of the passband in the bandpass characteristic of the bandpass filter.